1. Field of the Invention
The present invention relates generally to a signal processing apparatus, a signal processing method, a recording limiting apparatus and a recording limiting method suitable for use in accumulating bit streams inputted through a suitable means such as digital broadcasting and information networks on a recording media such as a disc. More specifically, this invention relates to a signal processing apparatus, a signal processing method, a recording limiting apparatus and a recording limiting method in which a packet indicative of attribute of data can be replaced satisfactorily when recording of inputted bit streams, for example, is limited.
2. Description of the Related Art
As a means for limiting recording of bit streams, there has so far been proposed a method of adding or deleting particular information to or from an orthogonal transform coefficient, for example (e.g. see cited patent reference 1).
[Cited Patent Reference 1]
Official Gazette of Japanese laid-open patent application No. 2001-223981
Satellite broadcasting, for example, transmits information such as image information and audio information in the form of digital signals and hence the thus transmitted image information and audio information are very high in quality. However, since image information and audio information are transmitted in the form of digital signals, personal computers and audio-video equipment become able to very easily handle data, and image information and audio information can easily be copied without deteriorating quality of information, which may cause a problem in a broadcasting program with a copyright.
Accordingly, in the satellite broadcasting, for example, a signal (attribute information) indicative of copy protect is encapsulated in advance into a copy guard program due to a restriction such as a copyright. When a receiver of the satellite broadcasting detects such signal, the receiver is requested to protect the above broadcasting program from being copied to other audio equipment than the receiver.
The above-mentioned copying is to record data outputted from the receiver to other equipment, and to temporarily store data in a suitable means such as a disc in order to process images for various services such as fast forward and rewind in the receiver is not included in the copying. For this reason, satellite broadcasting data has a signal for allowing the receiver to copy audio and video information (copy once).
Accordingly, when such data is transmitted from the receiver to the outside, in order to prevent illegal copying, a copy control signal (attribute information) should be changed from the above-mentioned “copy once” to “copy guard”.
It is customary that the copy control signal is provided as part of information called a Program Map Table (hereinafter referred to as a “PMT” for simplicity). On the other hand, in the satellite broadcasting, for example, a broadcasting program is generally transmitted in the form of a Transport Stream (hereinafter referred to as a “TS” for simplicity). The transport stream TS has data provided in the form called a “section”, and the PMT is contained in this section.
Further, the PMT has an arrangement shown in FIG. 2. As shown in FIG. 2 the value of Table ID is fixed to 02, and it is possible to judge the PMT by detecting this portion. Also, a SL (section length) indicates the length of this PMT and only the range shown by this section length SL is the PMT. Then, the copy control signal is contained in the descriptor shown in FIG. 2, and this portion should be rewritten in order to make copy free data become copy guard data.
As a method for rewriting such PMT, there have been so far used the following two methods. More specifically, according to the first method, all data are written on a recording medium such as a disc in a receiver and when a control circuit such as a CPU (central processing unit) searches data on the disc from the disc end and detects the PMT, the detected PMT is overwritten on the disc. According to the second method, when data is received by the receiver, the PMT is deleted in advance, and a signal indicative of the place of the PMT is flagged. Then, when the PMT is replaced, a new PMT is inserted into data based upon the signal indicative of such place of the PMT.
However, according to the first method, the control circuit has to search the data on the disc so that a load is imposed upon the control circuit, resulting in the performance of the whole of the receiver being lowered. Also, since a large-storage capacity disc becomes necessary, there is a risk that the first method becomes costly. Further, since an amount of processing to be executed by the control circuit such as the CPU increases as the receiver becomes higher in function, it becomes necessary to protect a load from being imposed upon the CPU as much as possible.
On the other hand, the second method in which the PMT is deleted in advance requires a circuit for deleting the PMT from the received stream data and a circuit for generating a signal indicative of the position of the deleted PMT in addition to the circuit for rewriting the PMT. There is then a risk that a circuit scale will become extremely large. Also, when the control circuit such as the CPU executes such processing, it is unavoidable that the load on the control circuit increases similarly to the above-mentioned first method. As described above, the related-art apparatus has encountered with the problems such as the increase of the loads on the control circuit and the requirements of the large-storage capacity disc, the special circuit and the increase of the cost, and hence it cannot replace the packet indicative of the attribute of the data satisfactorily.